See text Opahs, also commonly known as moonfish, sunfish, cowfish (not to be confused with Molidae), kingfish, and redfin ocean pan are large, colorful, deep-bodied pelagic lampriform fishes comprising the small family Lampridae (also spelled Lamprididae).

The family comprises two genera: Lampris (from Ancient Greek λαμπρός (lamprós) 'brilliant, clear') and the monotypic Megalampris[2] (known only from fossil remains).

[6] The six species of Lampris have mostly non-overlapping geographical ranges, and can be recognized based on body shape and coloration pattern.

[6] Opahs are deeply keeled, compressed, discoid fish with conspicuous coloration: the body is a deep red-orange grading to rosy on the belly, with white spots covering the flanks.

[8] Regional endothermy also arose by convergent evolution in tuna, lamnid sharks and billfishes where the swimming muscles and cranial organs are maintained at an elevated temperature compared with the surrounding water.

The gills are the main point of heat loss in fishes as this is where blood from the entire body must continuously be brought in close contact with the surrounding water.

Within the rete, the warm and cold blood flow past each other in opposite directions through thin vessels to maximise the heat transferred.

Unlike in billfish which have a specialised noncontractile tissue that functions as a brain heater, the opah cranium is heated by the contractions of the large eye muscles.

Lampris guttatus are able to maintain their eyes and brain at 2 °C warmer than their bodies, a phenomenon called cranial endothermy and one they share with sharks in the family Lamnidae, billfishes, and some tunas.

[12] The planktonic opah larvae initially resemble those of certain ribbonfishes (Trachipteridae), but are distinguished by the former's lack of dorsal and pelvic fin ornamentation.